The present invention is related to a motion enhancing mechanism that is well suited for use with flow control devices like the modulating actuator of a proportional control valve. The invention is particularly useful in valves intended for proportional, or modulating, control of fluid delivery within industrial processes making semiconductor devices, pharmaceuticals, or fine chemicals, and many similar fluid delivery systems.
The field of control valves intended for use within automated process control systems is broad and well known. Many proportional control valves have one or more moveable elements that may be actively positioned, anywhere between an extreme open condition and an extreme closed condition, to adjust the flow of fluid passing therethrough. Fluid delivery apparatus intended for manipulating process materials within semiconductor manufacturing equipment usually require attention to maintaining high purity of the delivered reactants and also are typically much smaller than valves used in petrochemical plants, for example.
Many different types of powered valve actuators are found in high purity instrumentation and control apparatus such as mass flow controllers. U.S. Pat. No. 4,695,034 issued to Shimizu et al. describes use of a stack of piezoelectric disc elements to effect movement of valve parts in a mass flow controller. U.S. Pat. No. 4,569,504 issued to Doyle describes use of a magnetic solenoid with interleaved magnetic circuit elements. U.S. Pat. No. 5,660,207 issued to Mudd describes use of a heated resistance wire that changes length with temperature to effect valve element movement. U.S. Pat. No. 6,178,996 issued to Suzuki describes use of a pressurized fluid, such as nitrogen gas, to control the degree of opening of a bellows-operated diaphragm-sealed control valve.
The patents mentioned above also illustrate a variety of moveable and fixed fluid pathway element combinations found in mass flow controller valves. Shimizu shows six different valve constructions wherein an approximately conical element translates toward or away from a circular opening having its axis aligned with the axis of said cone. Doyle shows a disk-shaped element, having a flat surface (colloquially called the seat) perpendicular to the valve axis of symmetry, which translates toward or away from an orifice surrounded by a narrow lip (together colloquially called the jet). Mudd shows a spherical gate-member which translates toward or away from a dished circular seat. Suzuki shows a combination of shapes which translate axially to change the conductance through fluid channels of the valve. Fluid dynamic characteristics of the variable geometry fluid pathway, formed by the combination of fixed and moveable valve elements, tend to dominate the relationship between actuator position and valve conductance.